The present invention relates to a drive unit, in particular a drive unit which is suitable for portable medical devices and with the aid of which movements to be carried out slowly can be automated.
In portable medical devices, e.g., glucose measuring devices, the automatic lancing of a body part and the subsequent automatic recovery of blood from the puncture site formed as a result of the lancing operation play an essential role. To convert electrical energy from a long-term electrical storage element specific to the glucose measuring devices, e.g., accumulators or batteries, into mechanical energy, electric motors or electromagnets are used, according to the prior art. With the aid of these drive units, either a pricking movement is executed directly or a secondary mechanical energy storage element, e.g., in the form of a spring, is charged and is subsequently highly dynamically discharged in order to generate the pricking movement (cf. DE 10 2004 037 270.5). In particular, the charging of a spring element which may be used as a secondary mechanical energy store or storage element requires a drive unit which is capable of applying the spring force or the spring torque necessary for prestressing a torsion spring. In order to apply these high forces and torques, e.g., direct-current motors used as electric motors are equipped with high-reduction gears.
The electric motors used hitherto in glucose measuring systems must normally be equipped with a gear in order to increase the torque for prestressing a secondary mechanical energy storage element. However, these gears have poor efficiencies, particularly when high step-up ratios are used. Moreover, these gears produce running noises and take up a large construction volume which, in glucose measuring devices, is available to only a very limited extent for reasons of simple handling. Moreover, gears with high step-up are mostly provided with metal gearwheels and with exact mountings, thus making them very costly to produce. Consequently, gears with high step-up, used for prestressing secondary mechanical energy storage elements, undesirably on the one hand considerably enlarge the dimensions of an integrated glucose measuring system and on the other hand considerably increase its production costs.
U.S. Pat. No. 4,383,195 discloses a piezoelectrically actuated snap fastener. A piezoelectric actuator contains a piezoelectric element. A snap device is disclosed, by means of which a force can be generated which is directed in the opposite direction to the expansion generated by the piezoelectric element. This force is a predetermined reaction force having to be overcome in order to trigger a snap-in of the snap device. The piezoelectric element comprises piezoelectric means for providing a force which opposes the snap connection and which overshoots the reaction force, and also means for applying an electrical field to the piezoelectric means, so that the force acting in the opposite direction can be generated and energy can be stored in the snap device, thus making the snapping of the device possible.
U.S. Pat. No. 6,313,566 relates to a piezoelectrically actuated motor. The piezoelectric motor disclosed contains a motor body and a layer connected to the motor body. Several small legs are connected to this layer in such a way that the small legs are attached to a substrate. Each of the small legs contains a piezoelectric wafer. The actuation of a piezoelectrically active wafer displaces a corresponding small leg in relation to the substrate. This displacement generates a transmission of energy to the layer. The energy stored in this way in the layer can be utilized in such a way that the motor moves along the substrate. The small legs are capable of moving independently of one another and are likewise capable of moving sequentially or within predetermined groups or units. The small legs may also be arranged in pairs, the individual small legs of a pair of small legs executing a simultaneous movement. The motor makes it possible to maintain a high holding force when the energy supply is absent.
In light of the outlined disadvantages of the prior art, it would be desirable to provide a drive unit with small external dimensions and an actuator which generates high actuating forces and which may be arranged within a portable measuring device to fulfill a plurality of functions.